1. Field of the Invention
The present invention relates to computer memory disk devices in which the speed of rotation is controlled, and particularly to reducing power consumption of multi-speed constant linear velocity and multi-speed constant angular velocity disk drives.
2. Description of the Related Art
It is known that reducing power consumption of computers and their peripherals promotes energy conservation. Further, it has been recognized that reducing power consumption of computer components and peripherals decreases the size of a power supply needed for this function. A smaller power supply facilitates the use of convenient portable computers, e.g., laptop and notebook computers. Thus, it is desirable to reduce the power required by computer peripherals in order to save energy and increase the convenience of computers.
It is known to reduce the voltage supplied to the head transport motor of a computer disk when no recording medium is loaded in the disk drive. U.S. Pat. No. 4,783,706 to Shoji et al. discloses such an arrangement. However, when a recording medium is in the disk drive then no power can be saved by using this method.
It is also known to xe2x80x9cspin downxe2x80x9d, i.e. stop spinning, a recording media when a disk drive has been inactive for a predetermined period of time. This results in a power savings, since the disk is idle. Such a method is shown in U.S. Pat. No. 5,197,055 to Hartung et al. However, a significant time delay is experienced when it is necessary to xe2x80x9cspin upxe2x80x9d the disk to reach operational rotational speed.
It is disclosed in U.S. Pat. No. 4,987,502 to Freeze, that random selection of successive disk tracks can be used to distribute head contact wear. The system counts idle periods in order to determine when to move the head. After a predetermined maximum number of idle periods has been reached the system employs a controller to stop the rotation of the disk. Stopping the rotation of the disk has the same effect on power consumption as the xe2x80x9cspin downxe2x80x9d method of the ""055 patent discussed above. Additionally, the disadvantage of a significant time delay to reach operational speed after stopping is also present when using the method disclosed in the ""502 patent.
Similar methods and arrangements for displacing the head to reduce wear are disclosed in U.S. Pat. No. 5,050,015 to Hack et al. and U.S. Pat. No. 5,117,315 to Nagasaki et al. The ""015 patent discloses moving the head to a waiting track or area outside the usable area of the magnetic tracks. The track location and waiting time are dependent on which tracks are read most frequently, since the objective of the ""015 patent disclosure is to reduce wear. A control circuit is stopped and started to achieve the displacement. Unfortunately, the stopping and starting of the electronic control circuit involves more power consumption. The ""315 patent discloses displacing the head when a processor detects presence or absence of rotation in the disk. The system is capable of reducing wear by slightly displacing the head two or three tracks and lifting the head when the disk is started. Power is saved by reducing the drag effect of the head inadvertently contracting the disk or start-up; however, the apparatus and method are not useful to save power when a disk is already in motion.
U.S. Pat. No. 4,658,308 to Sander discloses a method and apparatus for moving a head to a safe xe2x80x9chomexe2x80x9d position under microprocessor control when it is sensed that power to a rotating disk is to be interrupted. Slight savings in power are probably realized by reducing any inadvertent drag effects that would result if the head interfered with the disk rotation. However, the method and apparatus are ineffective to save power while a disk is spinning in a useful operation.
An objective of the present invention is to reduce the power consumption of an optical disk device without significantly degrading response time to a command to seek data.
Another objective of the present invention is to provide an apparatus and method for reducing power consumption that does not require removing a disk from the optical disk device.
The present invention is based on the inventors"" critical observation that power consumption can be reduced in an optical disk drive by determining when a period of inactivity occurs, and then issuing a command to reduce the velocity of the spindle motor which spins the disk medium to the lowest xe2x80x9coperational levelxe2x80x9d or just below the operational level, without completely stopping or xe2x80x9cspinning downxe2x80x9d the disk for the duration of the inactive period. The xe2x80x9coperational levelxe2x80x9d refers to that angular velocity where the head may still read or write data.
In a constant linear velocity (CLV) disk drive, a signal is issued from a microprocessor to an actuator to cause a head having read capability to seek to an outer track when a predetermined period of inactivity occurs. This is advantageous because the angular velocity of the disk medium is less at the outer periphery for a given constant linear velocity (the speed measured under the head), and therefore the power consumption of the spindle motor which spins the disk will be less.
In a constant angular velocity (CAV) disk drive a reduction of the rotational speed during a period of relative inactivity is accomplished by issuing a control signal from the microprocessor to the spindle control module to reduce the angular velocity of the spindle motor that spins the disk to the lowest operational level or just below the operational level without completely xe2x80x9cspinning downxe2x80x9d the disk for the duration of the inactive period.
Advantageously, in either embodiment, the disk is operational, as it is never completely xe2x80x9cspun downxe2x80x9d to the point that it stops rotating, with an exception for disks left inactive for large periods of time. So there is no associated significant delay in xe2x80x9cspinning upxe2x80x9d the disk upon receiving an I/O command. Thus, the invention can be used to reduce power consumption of a disk spindle motor while maintaining the disk in an operational mode, or spinning at a speed just below an operational mode. Regarding the mentioned exception, if the disk is left inactive for a predetermined time which is significantly long the disk may be stopped from spinning. The stopping of the disk, according to the present invention, will only follow the event of either moving the head to an outer track for CLV drives, or reducing the angular velocity to the lowest selectable speed for multi-speed CLV and multi-speed CAV drives.